Recent telecommunications technology has improved communication efficacy. Advanced methods of communications require creative solutions to problems encountered in implementing such advancements. Finite impulse response (FIR) filters are commonly used in high-speed data communications electronics for cancellation of interfering signals, such as echo, near-end crosstalk (NEXT) and far-end crosstalk (FEXT). Below is described a system for canceling echo.
A FIR filter is typically implemented by using a series of delays, multipliers, and adders to create the filter's output. The process of selecting the filter's length and coefficients is in the filter design, where the design effort should result in a frequency response which meets the desired specifications, including ripple and transition bandwidth, and optimize the filter's length and coefficients. The longer the filter (more taps), the more finely the response can be tuned, however the longer the filter, the more resources (power, circuitry, noise margin) are required to meet the performance requirements.
Currently, common data transceiver design includes an echo canceller that removes the undesired echo signal by creating a replica of the echo signal and subtracting it from the far-end generated signal. This method makes use of the fact that the echo signal is a linear function of a near-end transmitted signal, i.e. a given system with a given transmit signal produces a predictable echo signal. Therefore, a mathematical model of the echo signal based on the near-end data signal can be accurately built inside the echo canceller. However, often times the filter must include numerous taps to accommodate multiple operational circumstances, resulting in a lengthy filter that is over-designed, underutilized and burdensome to the system.
The near-end data signal is transmitted through an Adaptive Linear Filter, which produces an echo estimate. This echo estimate is then subtracted from the incoming signal, which is the sum of the desired far-end signal and the interfering echo signal, leaving the desired signal and any un-canceled echo. This data is recovered from this resulting signal. The difference between the resulting signal and the recovered data is used as the measurement of the error between the current and desired result, and can be used to adapt the filter's coefficients. This process is repeated until the error signal is minimized, and the echo estimate matches the echo as close as possible.
By examining the coefficient results of the Adaptive Linear Filter, it is possible to reconfigure the filter so that it is sufficient to cancel the interfering signal, but not to require the filter to have excessive dynamic range, unneeded bits of precision, excessive linearity or unneeded filter taps.
Accordingly, there is a need to develop a method of examining the coefficient results of the Adaptive Linear Filter to reconfigure the filter so that it is sufficient to cancel the interfering signal, but not to require the filter to have excessive dynamic range, unneeded bits of precision, excessive linearity or unneeded filter taps.